Personally, I believe that Peach is a defensive character and her playstyle revolves around stopping approaches with her turnips or safely pressuring opponents' shield with Floating Dair.
I love forcing opponents to stay in shield with some turnips, then go in with a grab. Down-throw can lead into an abundance of follow-ups (Bair, F-tilt, Side-B...), and it's the throw you want to go for at low percentages to rack up damage quickly.
Peach excels at edge-guarding, so when you catch opponents offstage, be brave and swoop in with a Floating Fair, Nair, or Dair. Or you can even stay onstage and try to snipe recovering opponents with turnips.
Most of my kills with Peach revolves around good edgeguards. If you can't secure a stock offstage, then try to land a Fair or a Smash. D-throw into Uair can kill at relatively high percentages if the opponent doesn't airdodge, or you can read an airdodge at around 85%~95% and charge an U-smash instead.
Other little strings like turnip into Fair or D-tilt into Fair can also land you a kill. And if you really need it, Peachy also has a semi-potent B-throw that you can use to kill with.
